Although the TSB mentioned only cracks on cylinder head, but the fact is Mazda is replacing the entire engine (or long block) for the problem doesn’t add up. Some members even been told by the Mazda dealer that the crack is on the back side of cylinder block. Either there’re more stories haven’t been told, or there will be more TSBs coming out for this problem.
As ridiculous as it might sound, this likely makes the most sense from Mazda's perspective.
It's easier to swap the engine completely for any affected units as newer engine assemblies will have any updated block and head castings typically of later model manufacturing design corrections.
From a maintenance standpoint, it's also easier to have the dealer swap in the whole assembly rather than having block surfaces checked and corrected, timing reassembled, etc. Mazda likely wants these vehicles processed as quickly as possible to avoid consumer backlash.
We have similar practices in aviation. Helicopters, especially military, have Quick Change Assemblies (QCAs) including the rotor system, transmissions and engine(s) all removable as a single assembly. The QCAs can be "hot swapped" for component failures, life retirement, etc and overhauled separately to reduce maintenance downtime and overall maintenance costs.
Quick turnaround makes for happier customers.
